U.S. patent number 8,156,763 [Application Number 12/084,857] was granted by the patent office on 2012-04-17 for method of producing glass.
This patent grant is currently assigned to AvanStrate, Inc.. Invention is credited to Kengo Maeda, Yukihito Nagashima.
United States Patent |
8,156,763 |
Nagashima , et al. |
April 17, 2012 |
Method of producing glass
Abstract
Provided is a method of producing a glass, including, in order
to obtain an excellent refining effect: preparing a raw glass batch
including: an antimony compound containing pentavalent antimony;
and an oxidizing agent (a cerium oxide, a sulfate, a nitrate); and
melting the raw glass batch. In preparing the raw glass batch, it
is preferable that the antimony compound be premixed with the
oxidizing agent. When the nitrate is used as the oxidizing agent,
the raw glass batch is prepared so as to include the antimony
compound in an amount of more than 0.5 parts by mass and at most 3
parts by mass, in terms of an amount of antimony pentoxide, per 100
parts by mass of a base glass composition expressed in terms of an
amount of an oxide.
Inventors: |
Nagashima; Yukihito (Tokyo,
JP), Maeda; Kengo (Mie, JP) |
Assignee: |
AvanStrate, Inc. (Mie,
JP)
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Family
ID: |
38048532 |
Appl.
No.: |
12/084,857 |
Filed: |
November 13, 2006 |
PCT
Filed: |
November 13, 2006 |
PCT No.: |
PCT/JP2006/322575 |
371(c)(1),(2),(4) Date: |
May 12, 2008 |
PCT
Pub. No.: |
WO2007/058146 |
PCT
Pub. Date: |
May 24, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090266111 A1 |
Oct 29, 2009 |
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Foreign Application Priority Data
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Nov 15, 2005 [JP] |
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2005-330811 |
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Current U.S.
Class: |
65/134.3; 501/27;
65/134.1; 65/134.9; 501/66 |
Current CPC
Class: |
C03C
3/091 (20130101); C03C 1/004 (20130101); C03B
1/00 (20130101) |
Current International
Class: |
C03B
5/225 (20060101); C03C 6/00 (20060101) |
Field of
Search: |
;501/27,66
;65/134.1,134.3,134.9 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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10 2004 026 257 |
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Nov 2005 |
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DE |
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1 199 287 |
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Apr 2002 |
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EP |
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10-114538 |
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May 1998 |
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JP |
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10-231139 |
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Sep 1998 |
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JP |
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11-035338 |
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Feb 1999 |
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JP |
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11-049520 |
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Feb 1999 |
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JP |
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2001-261370 |
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Sep 2001 |
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JP |
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2001-328820 |
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Nov 2001 |
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JP |
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2003-300750 |
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Oct 2003 |
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JP |
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2005-132713 |
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May 2005 |
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JP |
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2005-172881 |
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Jun 2005 |
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JP |
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Other References
Machine translation of JP 2005-172881 A, Jun. 30, 2005. cited by
examiner .
Machine translation of JP 11-035338 A, Feb. 9, 1999. cited by
examiner .
Machine Translation of JP 2005-132713 A, May 26, 2005. cited by
examiner .
Machine Translation of JP 2001-328820 A, Nov. 27, 2001. cited by
examiner .
Machine Translation of JP 11-049520 A, Feb. 23, 1999. cited by
examiner .
"Handbook of Glass Engineering", edited by M. Yamane et al.,
Asakura Shoten, 1999, p. 292, Partial English translation. cited by
other .
"Handbook of Glass Engineering", edited by T. Moriya et al.,
Asakura Shoten, 1963, p. 298, Partial English translation. cited by
other.
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Primary Examiner: Group; Karl
Assistant Examiner: Bolden; Elizabeth A
Attorney, Agent or Firm: Hamre, Schumann, Mueller &
Larson, P.C.
Claims
The invention claimed is:
1. A method of producing a glass, comprising: preparing a raw glass
batch comprising: an antimony compound containing pentavalent
antimony; and at least one oxidizing agent selected from the group
consisting of a nitrate and cerium oxide; and melting the raw glass
batch, wherein the raw glass batch is prepared by mixing the
antimony compound and the oxidizing agent so as to form a mixture
and then mixing the mixture with remaining materials of the raw
glass batch.
2. The method of producing a glass according to claim 1, wherein
the raw glass batch comprises the antimony compound containing
pentavalent antimony in an amount of more than 0.5 parts by mass
and at most 3 parts by mass, in terms of an amount of antimony
pentoxide, per 100 parts by mass of a base glass composition
expressed in terms of an amount of an oxide, where the base glass
composition expressed in terms of an amount of an oxide is a
composition of the raw glass batch in terms of an amount of an
oxide, excluding an amount of an oxide that serves as a refining
agent or an oxidizing agent.
3. The method of producing a glass according to claim 1, wherein
the raw glass batch is prepared, as a base glass composition
expressed in terms of an amount of an oxide, so as to substantially
have a composition of, expressed in mass percentage: 45 to 70% of
SiO.sub.2; 7.5 to 25% of Al.sub.2O.sub.3; 4 to 17.5% of
B.sub.2O.sub.3; 0 to 10% of MgO; 0 to 10% of CaO; 0 to 10% of SrO;
0 to 30% of BaO; 5 to 30% of MgO+CaO+SrO+BaO; 0 to 5% of ZnO; 0 to
5% of TiO.sub.2; 0 to 5% of ZrO.sub.2; 0 to 1% of Cl.sub.2; and 0
to 0.5% of SO.sub.3, where the base glass composition expressed in
terms of an amount of an oxide is a composition of the raw glass
batch in terms of an amount of an oxide, excluding an amount of an
oxide that serves as a refining agent or an oxidizing agent.
4. The method of producing a glass according to claim 1, wherein
the raw glass batch is prepared so as to obtain a glass having a
strain point higher than 575.degree. C., and a thermal expansion
coefficient in the range from 28.times.10.sup.-7/.degree. C. to
46.times.10.sup.-7/.degree. C.
5. The method of producing a glass according to claim 1, wherein
the raw glass batch is prepared such that a temperature at which a
viscosity of a molten material of the raw glass batch is
10.sup.2dPasec is equal to or higher than 1615.degree. C., and so
as to obtain a glass having a strain point higher than 630.degree.
C.
6. The method of producing a glass according to claim 1, wherein
the raw glass batch further comprises a tin oxide.
Description
TECHNICAL FIELD
The present invention relates to a method of producing a glass
characterized in its refining process, and particularly to a useful
method of producing an alkali-free glass.
BACKGROUND ART
In melting a glass raw material, a so-called refining agent is
added. A refining agent has, in general, the effect of growing
bubbles by a gas generation through its decomposition and thereby
promoting the removal of the bubbles contained in the molten glass
in the initial stage of the raw material melting process. In the
later stage of the melting process, the refining agent also has an
effect of absorbing the gas in residual minute bubbles and
promoting the elimination thereof.
In the case of an alkali-free glass, arsenic trioxide
(As.sub.2O.sub.3) has been used as such a refining agent. The
refining function of As.sub.2O.sub.3 is attributable to the effect
that As.sub.2O.sub.3 added to the raw material takes in oxygen from
the surroundings in the temperature raising process so that it
turns into As.sub.2O.sub.5, and then As.sub.2O.sub.5 releases the
oxygen when it turns back to As.sub.2O.sub.3 again at a higher
temperature. Therefore, when using arsenic trioxide as a refining
agent, an oxidizing agent is added into the glass raw material in
order to accelerate the change from As.sub.2O.sub.3 to
As.sub.2O.sub.5 in the initial stage of the melting reaction of the
material. As such an oxidizing agent, a nitrate commonly is
used.
Meanwhile, it is known that antimony trioxide (Sb.sub.2O.sub.3)
shows the same effect as As.sub.2O.sub.3. "Handbook of Glass
Engineering" (edited by Masayuki Yamane, et al., Asakura Shoten,
1999, p. 292) describes that antimony trioxide (Sb.sub.2O.sub.3) is
"less toxic than arsenic trioxide, and therefore has more often
been used instead of arsenic trioxide."
Recently, in various fields, there have been concerns about the
adverse impacts of the use of toxic substances on the environment.
Also in the field of an alkali-free glass mainly used for TFT
liquid crystal display substrates, the replacement of
As.sub.2O.sub.3, which has conventionally been used as a refining
agent, with more environment-friendly Sb.sub.2O.sub.3 has been
proposed (see, for example, JP10-114538A and JP10-231139A).
JP10-114538A discloses an alkali-free glass production method in
which As.sub.2O.sub.3 is not used as a refining agent,
characterized in that "0.05 to 2 wt % of SnO.sub.2 and 0.05 to 3 wt
% of Sb.sub.2O.sub.3 are added as refining agents."
JP10-231139A discloses an alkali-free glass production method in
which As.sub.2O.sub.3 is not used as a refining agent,
characterized in that "0.05 to 3 wt % of Sb.sub.2O.sub.3 and 0.01
to 2 wt % of a chloride in terms of Cl.sub.2 are added as refining
agents."
A compound containing pentavalent antimony sometimes is used as a
refining agent, not so often as antimony trioxide (Sb.sub.2O.sub.3)
that is a trivalent antimony oxide. "Handbook of Glass Engineering"
(edited by Taro Moriya, et al., Asakura Shoten, 1963, p. 298)
describes that "sodium antimonate
(Na.sub.2O.Sb.sub.2O.sub.5.1/2H.sub.2O) or sodium orthoantimonate
(Na.sub.3SbO.sub.4) have a refining effect."
JP11-35338A discloses "an antimony-based refining agent that is a
multiple oxide of pentavalent Sb and at least one element selected
from the group consisting of Mg, Zn, Ca, Sr, Ba, Li, K, Al, Si, Ti,
Sn, Zr, Ce, La, Nb and P."
JP11-49520A discloses "a glass melting method in which antimony
pentoxide is used as a refining agent." In this publication, it is
pointed out that when antimony pentoxide is used instead of
antimony trioxide as a refining agent, a nitrate that is an
oxidizing agent need not be added to change antimony trioxide into
antimony pentoxide, and thus if the nitrate need not be added,
melting segregation of a raw material caused by the addition of a
large amount of nitrate can be reduced (paragraph 0012).
JP11-49520A describes in its Examples the numbers of bubbles
measured when antimony pentoxide was added to raw glass batches.
Referring to this section, when 0.5 parts by mass of antimony
pentoxide was added per 100 parts by mass of the raw glass batch
(in terms of an oxide), the number of bubbles measured in the case
where a nitrate was not added (Example 3) was less than that
measured in the case where the nitrate was added (Example 2)
(Tables 2 and 3). Also from the viewpoint of melting segregation,
the case where the nitrate was not added (Example 3) was superior
to the case where the nitrate was added (Example 2) (Table 4). In
view of the above, in the method disclosed by this publication, a
nitrate should not be added when antimony pentoxide is used in a
raw material (Claim 2).
JP2001-328820A discloses "a glass production method in which a
batch of a cullet containing no arsenic oxide and a refining agent
other than arsenic oxide are melted to be formed." Examples of a
refining agent other than arsenic oxide include Sb.sub.2O.sub.5
and/or SnO.sub.2.
In the methods described in JP10-114538A, JP10-231139A and
JP11-49520A, there is still room for improvement to achieve the
required quality of bubbles in the case of a glass that is melted
at a high temperature like an alkali-free glass.
The "antimony-based refining agent" described in JP11-35338A has a
problem in that it is more expensive than antimony trioxide
(Sb.sub.2O.sub.3) and antimony pentoxide (Sb.sub.2O.sub.5), or that
it cannot be used depending on its composition.
In the method described in JP2001-328820A, there is a problem that
a sufficient refining effect cannot be obtained in the case of
melting a common mixture of glass raw materials with less content
of cullet.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a method of
producing a glass capable of solving the problems caused by the use
of an antimony oxide as an alternative refining agent to
As.sub.2O.sub.3, as well as reducing an amount of As.sub.2O.sub.3
to be used, preferably without using As.sub.2O.sub.3, while
ensuring an excellent refining effect.
The present invention provides a method of producing a glass,
including preparing a raw glass batch and melting the raw glass
batch. The raw glass batch includes: an antimony compound
containing pentavalent antimony; and at least one oxidizing agent
selected from the group consisting of a nitrate, a sulfate and a
cerium oxide. In this method, the raw glass batch is prepared by
mixing a mixture obtained by mixing the antimony compound and the
oxidizing agent with the remainder of the raw glass batch.
According to this production method, the preliminary mixing of the
oxidizing agent and the antimony compound containing pentavalent
antimony that serves as a refining agent enhances the cooperative
effects between the antimony compound and the oxidizing agent, so
that bubbles in the glass can be reduced.
Another aspect of the present invention provides a method of
producing a glass, including preparing a raw glass batch and
melting the raw glass batch. The raw glass batch includes: an
antimony compound containing pentavalent antimony; and a nitrate.
In this method, the raw glass batch includes the antimony compound
in an amount of more than 0.5 parts by mass and at most 3 parts by
mass, in terms of an amount of antimony pentoxide, per 100 parts by
mass of a base glass composition expressed in terms of an amount of
an oxide.
In the present description, the base glass composition expressed in
terms of an amount of an oxide is a composition of the raw glass
batch in terms of an amount of an oxide, excluding an amount of an
oxide that serves as a refining agent or an oxidizing agent.
Examples of an oxide that serves as a refining agent include an
antimony oxide, an arsenic oxide and a tin oxide. Examples of an
oxide that serves as an oxidizing agent include a cerium oxide.
In the above conversion in terms of an amount of an oxide, the
conversion is carried out so that the number of cationic atoms of
the composition does not change after the conversion. Therefore, 1
mol of calcium carbonate (CaCO.sub.3) is regarded as 1 mol of
calcium oxide (CaO). The same is applied to the conversion of an
antimony compound (into antimony pentoxide) to be described later.
Note that, in converting a raw glass batch in terms of an oxide, a
component that cannot be converted into an oxide (for example,
chlorine (Cl.sub.2)) is expressed as it is.
As disclosed in JP11-49520A, a nitrate causes a problem such as
melting segregation rather than enhancing the effect of reducing
the number of bubbles when it is used together with a relatively
small amount of (at most 0.5 parts by mass of) antimony pentoxide.
The study of the present inventors, however, has revealed that in
the case of using a relatively large amount of antimony pentoxide
as a refining agent, the use in combination with a nitrate improves
its refining effect.
Still another aspect of the present invention provides a method of
producing a glass, including preparing a raw glass batch and
melting the raw glass batch. The raw glass batch includes: an
antimony compound containing pentavalent antimony; and a sulfate
and/or a cerium oxide.
According to this production method, it is possible to reduce
bubbles in the glass by a cooperative effect between the antimony
compound containing pentavalent antimony that serves as a refining
agent and a sulfate and/or a cerium oxide that serves as an
oxidizing agent.
As described above, according to the present invention, it is
possible to produce a glass while ensuring an excellent refining
effect, even if the amount of As.sub.2O.sub.3 to be used is
reduced, or it is not even used.
BEST MODE FOR CARRYING OUT THE INVENTION
In the production method of the present invention, it is preferable
that the raw glass batch include an antimony compound containing
pentavalent antimony in an amount of more than 0.5 parts by mass
and at most 3 parts by mass, in terms of an amount of antimony
pentoxide, per 100 parts by mass of a base glass composition
expressed in terms of an amount of an oxide. The amount of the
antimony compound containing pentavalent antimony should be
evaluated after any compound containing pentavalent antimony is
converted into antimony pentoxide. In the production method of the
present invention, it is preferable that the raw glass batch
include an antimony compound containing pentavalent antimony in an
amount of more than 0.7 parts by mass and at most 3 parts by mass,
more preferably more than 1 parts by mass and at most 3 parts by
mass, particularly more than 1.5 parts by mass and at most 3 parts
by mass, and more particularly more than 2 parts by mass and at
most 3 parts by mass, respectively, in terms of an amount of
antimony pentoxide, per 100 parts by mass of a base glass
composition expressed in terms of an amount of an oxide.
As an oxidizing agent, at least one selected from the group
consisting of a nitrate, a sulfate and a cerium oxide is used. Two
or more of the above substances may be used as the oxidizing agent.
For example, it may include a nitrate as well as a sulfate and/or a
cerium oxide.
It is preferable, in the present invention, that the base glass
composition expressed in terms of an amount of an oxide be a
composition that is substantially free from an alkali metal oxide,
and particularly the following composition substantially. In this
description, the % expressions indicating components are all mass %
expressions.
45 to 70% of SiO.sub.2
7.5 to 25% of Al.sub.2O.sub.3
4 to 17.5% of B.sub.2O.sub.3
0 to 10% of MgO
0 to 10% of CaO
0 to 10% of SrO
0 to 30% of BaO
5 to 30% of MgO+CaO+SrO+BaO
0 to 5% of ZnO
0 to 5% of TiO.sub.2
0 to 5% of ZrO.sub.2
0 to 1% of Cl.sub.2, and
0 to 0.5% of SO.sub.3
The above composition may include less than 1%, preferably less
than 0.1%, of components typified by Fe.sub.2O.sub.3 and Na.sub.2O,
respectively, in addition to the above components. Particularly in
the industrial production of a glass, it is difficult to avoid in
some cases that the glass includes a small amount of impurities
derived from an industrial raw material. The term "substantially"
in the present description means that a small amount of a
component, that is, less than 1%, preferably less than 0.5%, and
more preferably less than 0.1% of the component, may be included.
Therefore, the phrase "a composition that is substantially free
from an alkali metal oxide" means a glass including less than 1% of
an alkali metal oxide.
In the present invention, it is preferable that the raw glass batch
be prepared so as to obtain a glass having a strain point higher
than 575.degree. C., and a thermal expansion coefficient in the
range from 28.times.10.sup.-7/.degree. C. to
46.times.10.sup.-7/.degree. C. In the present invention, it is more
preferable that the raw glass batch be prepared such that a
temperature at which the viscosity of a molten material of the raw
glass batch is 10.sup.2dPasec is equal to or higher than
1615.degree. C., and so as to obtain a glass having a strain point
higher than 630.degree. C.
As an oxidizing agent, a nitrate, particularly an alkaline earth
metal nitrate may be included. Preferably, the raw glass batch
includes the nitrate in an amount from 2.5 to 25 parts by mass,
more preferably from 7.5 to 25 parts by mass, and particularly from
9 to 25 parts by mass, per 100 parts by mass of the base glass
composition expressed in terms of an amount of an oxide.
As an oxidizing agent, a sulfate, particularly an alkaline earth
metal sulfate may be included. Preferably, the raw glass batch
includes the sulfate in an amount from 0.25 to 5 parts by mass, per
100 parts by mass of the base glass composition expressed in terms
of an amount of an oxide.
An alkaline earth metal (Group 2 element) to be added as a nitrate
and/or a sulfate may be any of Mg, Ca, Sr, and Ba. It is
preferable, however, that the raw glass batch is prepared so that
the amount of each metal and the total amount of these metals
included in the obtained glass are in the preferable ranges as
described above or to be described later.
As an oxidizing agent, a cerium oxide may be included. Preferably,
the raw glass batch includes a cerium oxide in an amount from 0.1
to 1 parts by mass, per 100 parts by mass of the base glass
composition expressed in terms of an amount of an oxide.
As a refining agent, a tin oxide may be included together with an
antimony compound. Preferably, the raw glass batch includes the tin
oxide in an amount from 0.05 to 1 parts by mass, per 100 parts by
mass of the base glass composition expressed in terms of an amount
of an oxide.
It is preferable that a refining agent and an oxidizing agent are
mixed prior to being mixed with other components of the raw glass
batch. More specifically, a mixture of the refining agent and the
oxidizing agent is prepared and then this mixture is mixed with the
remainder of the raw glass batch, so that the desired raw glass
batch is obtained.
In the method of the present invention, at least an antimony
compound containing pentavalent antimony is used as a refining
agent. As such an antimony compound, antimony pentoxide is
preferred. However, the raw glass batch may include an antimony
compound containing trivalent antimony such as antimony trioxide.
The present invention is particularly effective when it is applied
to a raw glass batch that is substantially free from arsenic
trioxide.
Hereinafter, the base glass composition of an alkali-free glass
that is preferably applicable to the present invention as well as
the reasons for the limitation thereof will be described.
SiO.sub.2 is an essential component for forming a glass network.
Less than 45% content thereof reduces the chemical resistance of a
glass as well as lowers the strain point of the glass, so that a
sufficient thermal resistance cannot be obtained. More than 70%
content thereof increases the viscosity of the glass at higher
temperatures, which causes difficulty in melting it. Therefore, the
lower limit of the SiO.sub.2 content is 45%, and preferably 50%.
The upper limit of the SiO.sub.2 content is preferably 70%.
Al.sub.2O.sub.3 is an essential component for restraining the
devitrification of a glass as well as for improving its thermal
resistance. Less than 7.5% content thereof easily causes the
devitrification. More than 25% content thereof lowers the acid
resistance as well as deteriorates the melting behavior. Therefore,
the lower limit of the Al.sub.2O.sub.3 content is 7.5%, and
preferably 10%. The upper limit of the Al.sub.2O.sub.3 content is
25%, and preferably 20%.
B.sub.2O.sub.3 is an essential component for improving the melting
behavior of a glass, for restraining the devitrification, and for
improving the chemical resistance, in particular the resistance to
a buffered hydrofluoric acid. Less than 4% content thereof
deteriorates the melting behavior of the glass as well as lowers
the resistance to a buffered hydrofluoric acid to an insufficient
level. More than 15% content thereof lowers the strain point of the
glass, thereby lowering the thermal resistance to an insufficient
level. Therefore, the lower limit of the B.sub.2O.sub.3 content is
4%, and preferably 7.5%. The upper limit of the B.sub.2O.sub.3
content is 17.5%, and preferably 15%.
At least one selected from the group consisting of MgO, CaO, SrO
and BaO is present, and the total content thereof is 5 to 30%. Less
than 5% of the total content thereof makes it difficult to melt a
glass. More than 30% of the total content thereof increases the
expansion coefficient of the glass excessively. Therefore, the
lower limit of the total content thereof is 5%, and the upper limit
thereof is 30%, and preferably 17.5%.
MgO is a component for improving the melting behavior of a glass
without much lowering the strain point. However, more than 10%
content thereof raises the devitrification temperature of the
glass. Therefore, the upper limit of the MgO content is 10%, and
preferably 7.5%.
CaO is a component having the same effects as MgO. More than 10%
content thereof raises the devitrification temperature of a glass.
Therefore, the upper limit of the CaO content is 10%.
SrO is a component capable of improving the melting behavior of a
glass without deteriorating the devitrification of the glass. More
than 10% content thereof increases the expansion coefficient of the
glass excessively. Therefore, the upper limit of the SrO content is
10%.
BaO is a component capable of restraining the devitrification of a
glass. More than 30% content thereof increases the expansion
coefficient of the glass excessively. Therefore, the upper limit of
the BaO content is 30%, and preferably 15%.
ZnO is a component capable of restraining the devitrification of a
glass as well as improving the melting behavior thereof. More than
5% content thereof lowers the strain point of the glass.
TiO.sub.2 can be contained up to about 5% within the range not
deteriorating the function of a glass as a display substrate.
ZrO.sub.2 is a component whose inclusion is desired because it
raises the strain point of a glass as well as improving the acid
resistance and the alkali resistance. However, more than 5% content
thereof easily causes the striae and devitrification as well as
deteriorates the melting behavior.
Cl.sub.2 is a component that has a refining effect and can remain
in a glass as long as its content is up to 1%, and preferably up to
0.5%.
SO.sub.3 is a component that can remain in a glass up to 0.5% as a
remainder of a sulfate to be used as an oxidizing agent.
Summarizing the above, a glass to which the present invention more
preferably can be applied (base glass composition expressed in
terms of an oxide) consists substantially of the following
components, when expressed by mass % again:
50 to 70% of SiO.sub.2
10 to 20% of Al.sub.2O.sub.3
7.5 to 15% of B.sub.2O.sub.3
0 to 7.5% of MgO
0 to 10% of CaO
0 to 10% of SrO
0 to 15% of BaO
5 to 17.5% of MgO+CaO+SrO+BaO
0 to 5% of ZnO
0 to 5% of TiO.sub.2
0 to 5% of ZrO.sub.2
0 to 0.5% of Cl.sub.2, and
0 to 0.5% of SO.sub.3
EXAMPLES
Examples 1 to 6
A raw glass batch for each Example was prepared so that it has a
base glass composition shown in Table 1 and includes a refining
agent and an oxidizing agent shown in Table 2. As described above,
the base glass composition was calculated by excluding oxides
(Sb.sub.2O.sub.5, SnO.sub.2) that serve as refining agents and an
oxide (CeO.sub.2) that serves as an oxidizing agent. A sulfate and
a nitrate shown in Table 2 were added as alkaline earth metal
salts. Therefore, the alkaline earth metals contained in these
salts were counted as oxides in the base glass composition.
TABLE-US-00001 TABLE 1 Component SiO.sub.2 Al.sub.2O.sub.3
B.sub.2O.sub.3 MgO CaO SrO BaO Mass % 60.5 15.0 7.5 1.5 5.5 4.0
6.0
As a raw material for the sulfate, a calcium sulfate was used, and
as raw materials for the nitrate, magnesium, strontium and barium
nitrates were used. The remainders of the raw materials of
magnesium, calcium, strontium and barium were their carbonates. As
other materials, a silica powder, an alumina, a boric acid, and a
cerium oxide were used. As the refining agents, oxides (antimony
pentoxide and stannic oxide) were used.
Furthermore, in each of Examples 2 and 6, the antimony pentoxide
and the oxidizing agent previously were mixed (premixed) before
they were mixed with the base glass raw material. Then, the mixture
obtained by the premixing was mixed with the remainder of the raw
glass batch.
TABLE-US-00002 TABLE 2 Example 1 Example 2 Example 3 Example 4
Example 5 Example 6 Refining agent Sb.sub.2O.sub.5 2.0 2.0 2.0 2.0
2.0 2.0 SnO.sub.2 -- -- 0.1 -- 0.1 0.1 Oxidizing agent CeO.sub.2
0.48 0.48 -- -- -- -- sulfate -- -- 1.5 -- -- -- nitrate -- -- 5.1
16.2 16.2 Premixed -- Yes -- -- -- Yes Number of bubbles 140 120
150 200 80 50 (pieces/100 g) (Components are expressed by mass % in
this table)
After each of the batches prepared as described above was melted in
an electric furnace at 1600.degree. C. for 4 hours using a platinum
crucible, the molten material was poured onto a stainless steel
plate and formed into a plate-like shape, and then cooled down to a
room temperature. The number of bubbles contained within an area of
5 cm square in the center of each obtained glass was measured using
an optical microscope, and then converted into the number thereof
per 100 g. The respective results are shown in Table 2.
Comparative Examples 1 and 2, and Reference Example 1
Comparative Example 1 is an example where trivalent antimony was
used as the refining agent. Comparative Example 2 is an example
where pentavalent antimony was used as the refining agent. Note
that Reference Example 1 is an example where arsenic trioxide
(As.sub.2O.sub.3) was used as the refining agent.
Base glass raw materials for Comparative Examples 1 and 2 as well
as Reference Example 1 were prepared respectively in the same
manner as in Examples. The refining agent and the oxidizing agent
were added in the mass percentages shown in Table 3, to 100 parts
by mass of each of these base glass raw materials in the same
manner as in Examples, so that the batches for Comparative Examples
and Reference Example were prepared respectively. Note that in
these Comparative Examples and Reference Example, no other
oxidizing agents (such as a sulfate) were added.
TABLE-US-00003 TABLE 3 Comparative Comparative Reference Example 1
Example 2 Example 1 Refining agent As.sub.2O.sub.3 -- -- 1.2
Sb.sub.2O.sub.3 2.0 -- -- Sb.sub.2O.sub.5 -- 2.0 -- Total amount of
Sb (2.2) (2.0) (--) Oxidizing agent 9.4 0 9.4 nitrate Number of
bubbles 280 270 30 (pieces/100 g) (Components also are expressed by
mass % in this table. The total amount of Sb denotes the total
amount of all the antimony oxides in terms of antimony pentoxide
(Sb.sub.2O.sub.5).)
These batches were melted in the same manner as in Examples so as
to obtain glass samples. The numbers of bubbles also were measured
in the same manner, and the respective results also are shown in
Table 3.
Note that since Comparative Example 1 is an example where antimony
trioxide (Sb.sub.2O.sub.3) was used, the amount thereof in terms of
antimony pentoxide (Sb.sub.2O.sub.5) that is a pentavalent antimony
compound also is shown in this table.
The above results of Examples and Comparative Examples show the
following.
As is apparent from the results of Examples and Comparative Example
2, it was observed that in the case where a relatively large amount
of antimony pentoxide was added, the addition of the oxidizing
agent, particularly a cerium oxide or a sulfate, together with the
antimony pentoxide significantly improves the refining effect.
As is apparent from the results of Examples 4 and 5, the use of a
sufficient amount of the oxidizing agent as well as the further
addition of a tin oxide produce a more marked refining effect.
Furthermore, in Example 6, although no arsenic trioxide was added,
the premixing performed in addition to the preparation in Example 5
resulted in the number of bubbles similar to that obtained in
Reference Example 1 where arsenic trioxide was used.
Comparisons between Examples 1 and 2 as well as Examples 5 and 6,
respectively, showed that the premixing of the antimony pentoxide
and the oxidizing agent before their mixture with the base glass
raw material reduces the number of bubbles in the molten glass.
The thermal expansion coefficients of the glass samples obtained in
respective Examples were in the range from
28.times.10.sup.-7/.degree. C. to 46.times.10.sup.-7/.degree. C.
(about 37.times.10.sup.-7/.degree. C.), and their strain points
were 630.degree. C. or higher (about 670.degree. C.). The
temperature at which the viscosity of the molten material of the
raw glass batch in each Example was 10.sup.2dsec was equal to or
higher than 1615.degree. C. (about 1655.degree. C.). Note that the
thermal expansion coefficients were measured according to JIS R
3102. The strain points were measured according to JIS R 3103. The
viscosities were measured according to JIS R 3104.
INDUSTRIAL APPLICABILITY
The present invention provides a method of producing a glass with
an excellent reduction of bubbles with minimal use of arsenic
trioxide, and thus has many applications in the field of glass
production technology.
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